The present invention relates to electrophotocopiers, and more particularly to cleaning charging and transfer rollers used in electrophotocopiers.
In conventional electrophotography, a photoconductor is electrostatically charged uniformly over its surface and is exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas of the photoconductor. The undischarged areas of the photoconductor thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern. The latent electrostatic image may then be developed by contacting it with a finely divided, electrostatically attractable toner material, such as a resinous powder. The toner is held in the image areas by the electrostatic fields on the photoconductor. Where the field is greatest, the greatest amount of toner is deposited, and where the field is least, little or no toner is deposited. Thus, a toned image is produced in conformity with the latent electrostatic image. The toner is subsequently transferred to a sheet of plain paper or other surface and suitably affixed to thereby form a permanent print.
The toner may be fixed by passing the sheet of paper or other surface including the toned image between a heated roller and a second roller in pressure contact therewith whereby the toner becomes fused to the sheet of paper.
The toned image is generally transferred to a plain paper copy sheet by passing the copy sheet between the photoconductor including the toned image and a charged, transfer roller in contact therewith. The transfer roller is charged electrically opposite that of the toner, but with a greater potential than that of the photoconductor so that the toner particles are attracted towards the roller. Thus, when a copy sheet is interposed between the roller and the toner covered photoconductor, the toner particles, being attracted by the charged transfer roller, are transferred to the copy sheet.
In the event a copy sheet is not passed between the charged transfer roller and the photoconductor after the image on the photoconductor has been developed, the residual toner particles on the photoconductor will be transferred nevertheless, but now instead of to the copy sheet, to the transfer roller. As a result, a buildup of toner particles on the transfer roller occurs, causing the back surfaces of subsequently passed copy sheets to be smeared with toner from the transfer roller. A similar problem is encountered with the charging roller, which also becomes contaminated with toner particles which are not removed by the cleaning system for the photoconductor.
The instant invention therefore provides a multiple roller assembly wherein charging or transfer rollers can be moved in and out of operational and functional positions to facilitate cleaning of one roller while another roller performs its operational function, thereby overcoming the foregoing problems.